a bit like cameras in ATMs
Some years ago the banks were getting complaints about "phantom withdrawals" from cash machines, the customer denying having used the machine. The banks started fitting cameras. Subsequent complainants, shown the footage suddenly remembered the occasion - or recognised a "friend", family member or colleague.
"We are all innocent until until proved guilty" but when we are guilty, absence of evidence doesn't make us innocent. Denying the opportunity to collect evidence only benefits the guilty.